The influence of surface crystallography and applied potential on the thiol-exchange procedure to create mixed alkylthiol DNA SAMs is detailed. A single crystal gold bead and fluorophore labeled thiol modified DNA were used to characterize the resulting surface modifications. The thiol-exchange occurs with different efficiencies on the low index planes ( 111,100,110) as compared to 311 and 210. Positive applied potentials (>0/SCE) result in 10 x higher coverage than when compared to deposition at the open circuit potential (OCP) over the same 60 min time period. Negative potentials (<0/SCE) resulted in less uniform coverage with the 111 facet being significantly modified. The electrolyte used during the deposition was a 10 mM TRIS Buffer with 100 mM NaCl 500 mM MgCl2. The influence of [Cl-] was studied showing it had a significant impact on the thiol-exchange at the positive potentials, where higher [Cl-] resulted in higher DNA coverages and a more uniform coverage across the multi-crystalline surface. The local environment of the thiol-exchanged DNA SAMs were compared for different regions on the surface using potential driven DNA reorientation modulating the fluorescence intensity. These results showed a common behaviour from all surfaces suggesting that the DNA SAMs prepared by thiol-exchange were consistently prepared with a variable surface concentration controlled by potential and time. (c) 2017 Elsevier Ltd. All rights reserved.